空间角度复合应变估计中的运动伪影产生因素研究

Influence of Factors on Motion Artifacts in Strain Estimation with Spatial Angular Compounding

颈动脉弹性成像可用于分析动脉内斑块的应变分布,并对其破裂风险(即易损性)进行有效评估。空间角度复合(Spatial Angular Compounding,SAC)方法已被提出来进一步改善其应变估计的性能。然而,在SAC各个角度的发射、接收过程中,斑块的运动和形变可能会导致运动伪影。因此,本研究的目的是通过仿真实验对基于SAC的应变估计中导致运动伪影产生的因素进行研究,包括脉冲重复频率(Pulse Repetition Frequency,PRF)和偏转角度数量(Number of Steering Angle,NSA)。在仿真实验中,物体被施加一个恒定速率为2s^(-1)的轴向压缩,来模拟理想情况和有运动伪影情况下的成像过程。本研究分析了PRF为200 Hz～10 kHz和NSA为1、3、5和7时的SAC应变估计性能,并通过信噪比(Signal-to-Noise Ratio,SNR)和对比度噪声比(Contrast-to-NoiseRatio,CNR)进行定量评估。结果表明,当PRF<4 kHz时,SNR和CNR会随PRF增加而增加,之后趋于平稳。对比不同角度SAC的结果发现,当PRF<1 kHz时,角度数越少,SNR和CNR越高;当PRF>4 kHz时,不同角度SAC的SNR和CNR皆比较接近。综上,本研究评估了PRF和NSA对SAC方法在应变估计中的影响。对于颈动脉弹性成像,基于PRF>4 kHz和NSA=3的SAC可以获得运动伪影较小的应变图像。

Carotid elastography can obtain the strain distribution of carotid atherosclerotic plaques and evaluate the vulnerability of plaques. Spatial angular compounding(SAC) has been proposed to improve the performance of strain estimation in carotid elastography. However, the motion and deformation of the plaque during multi-angle acquisitions may cause motion artifacts. In this study, the factors introducing motion artifacts in the strain estimation, including the pulse repetition frequency(PRF) and number of steering angle(NSA) were analyzed in the simulation experiments. In order to mimic the motion and deformation of the plaque, a constant axial compression at the strain rate of 2 s-1 was applied during the imaging process. The PRF was set from 0.2 kHz to 10 kHz and the NSA was set to 1, 3, 5 and 7. The elastographic signal-tonoise ratio(SNR) and contrast-to-noise ratio(CNR) were used to quantitatively evaluate the quality of strain estimation. The results showed that, the SNRs and CNRs increased with the PRF when PRF<4 kHz, and then remained constant. Comparing the performance of NSA=3, 5 and 7, the SNRs and CNRs were higher with a smaller NSA when PRF<1 kHz. When PRF exceeded4 kHz, the performance of SAC with different NSAs became similar in terms of SNRs and CNRs. In conclusion, this study has investigated the influence of the PRF and NSA on motion artifacts of strain imaging with SAC. In carotid elastography with SAC, the strain images with less motion artifacts are obtained when NSA is 3 and PRF>4 kHz.